code: def test_HandleMissingIgnore_ExpectMappingUsed(self):
      train = pd.DataFrame({"city": ["Chicago", np.NaN, "Geneva"]})
      expected_result = pd.DataFrame(
          {"city_1": [1, 0, 0], "city_2": [0, 0, 1]}
      )
  
      encoder = encoders.OneHotEncoder(handle_missing="ignore")
      result = encoder.fit(train).transform(train)
      expected_mapping = pd.DataFrame(
          [
              [1, 0],
              [0, 1],
              [0, 0],
              [0, 0],
          ],
          columns=["city_1", "city_2"],
          index=[1, 2, -2, -1],
      )
  
      pd.testing.assert_frame_equal(expected_result, result)
      pd.testing.assert_frame_equal(
          expected_mapping, encoder.category_mapping[0]["mapping"]
      )
  
imports: import pandas
  from unittest import TestCase
  import numpy
  import tests.helpers
  import category_encoders
label_desc: Use image node_id 13 for calling the TestOneHotEncoderTestCase obj's underlying member method code with example usage: obj.test_HandleMissingIgnore_ExpectMappingUsed() without return types